Summary:
The South Arturo Mine is located in the northern end of the Carlin Trend, a 40 mile-long north-northwest alignment of sedimentary rock-hosted gold deposits. These deposits are generally known as Carlin-type deposits named after the Carlin deposit. More than 50 million ounces of gold have been mined from the Carlin Trend since 1980. Characteristically, the gold mineralization in the Carlin-type gold deposits is dispersed, micron-sized, and found commonly on the rims of pyrite grains in predominately carbonate-bearing host rocks. Decalcification, silicification, and dolomitization are the most dominant alteration features. Generally, there is negligible base metal content, low silver to gold ratios, and a geochemical enrichment in arsenic, antimony and mercury.
The South Arturo gold-silver deposits can be divided into five mineralized areas. These areas are the South Arturo, West Button Hill, Southwest Dee pit, Deep North, and Hinge. The majority of these deposits are classified as “Meikle Type” breccia hosted Carlin type deposits. A complex set of breccias occur at the upper contact of the Bootstrap limestone. These breccias can be generalized into four basic types: silicified heterolithic breccias, silica-Sulfide breccia, dolomite breccia, and cavity- fill breccias. While mineralization is widespread throughout the South Arturo Mine area, localized high-grade gold mineralization drives the economics and mine locations.
South Arturo
The northern extent of South Arturo mineralization lies approximately 200 feet southeast of the Dee pit and under 600 feet of waste rock. An overall north-south orientation to mineralization is inferred from the grade thickness contours, which define an area 1,700 feet in a north-south direction by 300 feet to 350 feet wide in an east-west direction. The mineralization and Tertiary contact dip 15° to 20° to the south. Drilling has shown that rocks are oxidized to a depth of up to 2,000 feet. Paleozoic rocks host the mineralization mainly in multi-stage, multi-lithic breccias with gold values ranging from 0.006 opt Au. These breccias are commonly formed by karsting or dissolution of carbonate rock and subsequent collapse and cavity fill. In general, decalcification is followed by weak to strong silicification with local argillization. Silver to gold ratios are generally 1:1 at grades of greater than 0.06 opt Au but increase to 5:1 at lower gold grade values.
Dee Deep North
Dee Deep North is a north-northeast trending pod of mineralization that plunges slightly north and is approximately 600 feet long, 150 feet wide, and 150 feet thick. The majority of high-grade refractory mineralization is in silica-Sulfide breccia within a flat to west-dipping silicified, multilithic breccia body above the Bootstrap limestone between 4,900 FASL and 5,100 FASL. The principal controls are the north-northeast trending high angle EB fault and southwest dipping low-angle structures.
Southwest Dee
The Southwest Dee pit mineralization is along the north-northeast trending, west dipping Dee Fault Zone. The mineralization is carbonaceous, partially oxidized, variably silicified mudstone/siltstone breccia approximately 300 feet in a north-south strike length, 100 feet wide, and 150 feet in thickness. The mineralization sits between 4,900 FASL and 5,100 FASL, with a small portion exposed along the southwest high wall at the bottom of the Dee pit.
West Button Hill
The West Button Hill mineralization trends north-northeast for over 2,000 feet in strike length, in pods that vary up to 600 feet wide and 50 feet thick. The majority of high-grade refractory mineralization is in the lower Rodeo Creek Formation and multi-lithic breccias above the Bootstrap limestone. The principal controls are the north-northeast and north-south trending high-angle structures and favorable host rocks. The mineralization has been shown to extend 1,230 feet below pre-mining surface elevation, as it is offset on the northeast striking, down-to-the-east Tara West fault.
Hinge
The Hinge zone is a north-south striking zone that lies between the Arturo zone to the south west and West Button Hill to the northeast and is due east relative to the existing Dee pit. It is approximately 1,400 feet long and up to approximately 300 feet wide, lying between elevations of 4,750 FASL and 5,250 FASL at depths from 330 feet to 900 feet below surface. Mineralization is hosted in the lower portion of the Rodeo Creek Formation and silicified breccias of the Basal Rodeo Creek and Popovich Upper Mud units. Breccia bodies drape the Bootstrap limestone. Mineralization in the Hinge zone is controlled by the Hinge fault, a steeply east dipping northsouth structure that appears to be a northerly extension of faults in Newmont’s Bootstrap pit to the south. Intersecting faults that influence mineralization have not been clearly identified. Much of the mineralization is partially to completely oxidized, even in the more deeply buried zones.